We present a systematic study of both the temperature and frequency dependence of the optical response in TaAs, a material that has recently been realized to host the Weyl semimetal state. Our study reveals that the optical conductivity of TaAs features a narrow Drude response alongside a conspicuous linear dependence on frequency. The weight of the Drude peak decreases upon cooling, following a $T^2$ temperature dependence, in good agreement with theoretical predictions. Two linear components with distinct slopes dominate the low-temperature optical conductivity. A comparison between our experimental results and theoretical calculations suggests that the linear conductivity below $\sim 230 {\text{cm}}^{-1}$ arises purely from interband transitions near the Weyl points, providing rich information about the Weyl semimetal state in TaAs.

• Received 1 October 2015
• Revised 1 February 2016

DOI:https://doi.org/10.1103/PhysRevB.93.121110